A muscular, middle-aged guy
comes home with one of his friends. Together, they approach his hot wife, who happens
to be lying on the couch and wearing the shortest dress she owns. She forgot to
wear underwear. Again. The husband makes a proposition: Turns out, he's always
fantasized about watching her have sex with another man. Would she consider doing
so with his friend?

She gives the friend a
once-over. He is even more muscular than her husband. His erection is nearly
bursting out of his pants. She comments on its size, grins and asks her husband,
"Are you sure this is what you want?" He nods, takes a seat and begins masturbating
while his wife eagerly goes down on the other man. They proceed to have the
hottest, loudest sex of her life right before her husband's eyes.

If you've ever
browsed Xtube or PornHub, you have undoubtedly seen this and other so-called
"cuckold" scenarios played out over and over again. But why would porn made by,
and for, heterosexual guys so often depict men who take pleasure in letting
other men have sex with their wives?

The answer, in
part, is because there's a huge demand for it. In an age where pornographers are
practically responding to viewers' demands in real-time, porn-consumers have made
it clear that watching someone's wife bang a random guy is a top priority. When
neuroscientists Ogi Ogas and Sai Gaddam analyzed the contents of a billion online search
terms as research for their 2012 book A Billion Wicked Thoughts, they discovered
that "cuckold porn" is second only to "youth" in heterosexual porn searches. (For
the more literary-minded, a quick search for "cuckold erotica" on Amazon yields
hundreds of books, including such clever titles as The Cuck Club and Lucky Cucky.)

But it's not just
the market for cuckold content that bears out the trend. Believe it or not, guys
on the internet constantly send me their fantasies about watching some stranger
give it to their wife. "It turns me on to think about my wife having sex with
another man," one guy wrote. "And not just OK sex, but wild, passionate, and
very satisfying sex for her." Another wrote, "I wish I could take my wife to
sex clubs so that I could watch her have sex with other men."

Allow me to
explain. As a sexologist, I'm fascinated by what turns people on and why. For
the past two years, I've invited visitors to my website to describe their most compelling sexual fantasies through an anonymous form. Not surprisingly, I get the obligatory desires for
more traditional threesomes and orgies, not to mention a lot of interest in
bondage, forced sex, cross-dressing and exhibitionism. There also have been
more than a few Harry Potter-themed fantasies.

But more than anything,
I've been inundated with tales from men eager to watch their wives or
girlfriends take it from other guys. It's almost always watching without
participating, and usually, it's important that the other guy have a bigger
penis. Often, these guys aren't writing just to share their fantasy; they're
anxious to find out if this desire is "normal" or healthy for an otherwise
sexually fulfilled straight guy in a committed relationship.

Without delving
into the issue of what it means for a fantasy to be "normal," my answer to
these men, should I have to wager a professional opinion, is that it's perfectly
fine to entertain this one. But not for the reasons you might expect.

From an
evolutionary perspective, the idea that a guy would take pleasure from watching
his wife with another man is counterintuitive. Historically, men have gone to
great lengths to avoid being "cuckolded," or finding their wives impregnated by
someone else. Not only does cuckoldry limit men's ability to "spread their seed,"
but it forces them to expend scarce resources raising someone else's kids. The
fear of cuckoldry is thought to be a key factor that shaped how our male
ancestors approached sexual relationships and, to this day, is considered by
many scientists to be the reason men tend to get more jealous (often violently
so) about their partners' sexual infidelity than women.

Of course, men have
less to fear from cuckoldry today. Birth-control advances and paternity tests
can put men's minds at ease. But cuckold fantasies aren't unique to the modern
era. They were documented in the writings of Freud and others long before the pill
was ever invented—so we know men today aren't into cuckoldry just because it
has become "safe."

In the popular
discourse, there's no shortage of theories on the origins of cuckold fantasies,
or troilism in the vocabulary of
psychologists. Columnist Dan Savage has advanced the notion that these
fantasies are an eroticization of a man's anxiety that his wife will cheat. In
other words, men cope with the threat of infidelity by turning the fear into
something sexually arousing. More recently, journalist Anneli Rufus argued that troilists are just masochists who "revel in the psychological agony"
of the humiliating situation.

But psychologists
don't buy either argument. Eroticization is a strategy rarely taken with other
fears. So why would it be so specific to cheating? Plus, while the
troilism-as-masochism argument might apply in some cases, it proves weak when
you consider that most cuckold fantasizers rarely desire other masochistic acts
(like being whipped or flogged), and their interests tend to emerge in
adulthood, unlike sadomasochists whose interests tend to develop in the early
teenage years.

Increasingly,
scientists favor a biological explanation based on a growing body of work on sperm competition. Research shows that when one woman mates
with several men, those men can display behavioral and biological changes
intended to increase their likelihood of fertilizing her egg—without even realizing
it. For example, when men masturbate to porn featuring multiple men
having sex with the same woman, their ejaculate contains more active sperm than
it does when they beat off to an all-female threesome, according to a 2005 study of 52 men. Other research has found that men
report thrusting faster and deeper during sex when they suspect their female
partner has cheated, presumably as a way of displacing rival sperm. These
findings suggest the provocative possibility that men are "wired" to find
cuckold scenarios arousing because they promote behaviors that help their own
sperm win a raging intra-vaginal sperm war.

Not everyone is
convinced that sperm competition is the key, though. "I think of it as the
'King Bee Syndrome,'" David Ley, psychologist and author of Insatiable Wives: Women Who Stray and the
Men Who Love Them, explained over e-mail. Many men he's encountered simply get off on
the notion of other guys desiring their wives. They think to themselves, "'Look
what a hot, sexy woman I've got' and how that reflects on the man's power," Ley
says. "Displaying and sharing one's sexy wife is a status symbol."

That said, cuckold
fantasies might have multiple motivations, and the factors involved might not
be the same across individuals. Social and cultural norms likely play a role in
shaping these fantasies, too. Indeed, internet search trends reveal that
interest in cuckold porn has surged in the last decade, which, according to
Ley, "reflects a complex interaction of female sexual and economic liberation,
technology breaking down privacy and secrecy walls, changing marriages and more
liberal sexual values." The internet has been instrumental in providing pornographic
validation and a sexual outlet for men with cuckold fantasies; it also enables
couples to easily recruit no-strings-attached third wheels to explore these
fantasies in real life.

Based on my reading
of the science, cuckold fantasies appear to be a normative male sexual desire. But
should men act upon such fantasies? Ley warns that "these fantasies draw upon powerful
emotions and social programming that shouldn't be treated casually or without
careful thought." Bringing other people into your bed has the potential to
affect your sex life and marriage in ways both good and bad after the action
stops—a reality which porn videos have the luxury of avoiding.